Non-monotonic evolutionary patterns of aerosol transmission risk in dynamic density medical units

The infection control efficacy of fixed ventilation systems in hospital wards exhibiting dynamic staff densities remains unclear, necessitating further elucidation of the synergistic effects among staff density, spatial layout, and ventilation conditions on aerosol transmission risk. This study employed in-situ measurements and multi-parameter coupled analyses within clinical wards to examine the dynamic relationships between airflow organization, pollutant transport, and exposure risk across three densely occupied ward typologies, while evaluating the potential of airflow rate adjustments to enhance contamination control. Key findings demonstrate that the ward layout and staff density collectively govern pollution pattern restructuring: high staff occupancy wards are prone to ventilation blind zones due to airflow reorganization, generating dynamic pollution hotspots within obstacle vortex regions, nevertheless, the relative magnitude of pollutant concentrations in the key staff activity areas showed spatial stability. Subsequent quantitative analyses revealed that aerosol suspension rates initially decrease then increase with rising staff density, while deposition rates exhibit the inverse trend, highlighting limitations in single-mode risk assessment models. Notably, despite ventilation intensification reducing indoor contamination, deposition rates in optimized high-density wards remained 4.7–6.8 times higher than in unoptimized single rooms, establishing a clear efficacy boundary for unilateral ventilation strategies. These findings underscore the necessity for synergistic interventions integrating layout optimization (eliminating airflow dead zones), targeted decontamination (highly enriched surfaces), and dynamic personnel flow management, thereby advancing the theoretical foundation for hospital infection control engineering design.